Protection and control

Protection components are rarely right in isolation. A relay is chosen for the protection scheme, an instrument transformer for the relay it feeds, and a breaker for the fault level it must interrupt. A device that is correct on its own and wrong for the scheme is still wrong.

For a replacement, the existing arrangement governs. Ask what the new device has to be compatible with. The nameplate of the old one usually answers most of it.

Protection and control types

Vacuum, air and moulded case circuit breakersMedium voltage vacuum breakers and low voltage air and moulded case breakers, new or as replacements.Protection, control and relay panelsRelay, control and marshalling panels built to the scheme drawings.Protection relaysNumerical feeder, transformer and motor protection, specified against the scheme.

Documents normally requested

For a replacement, send the nameplate, model and firmware version of the existing device.

Delivery and logistics

Devices are lighter to move than transformers and switchboards. The harder part of the delivery is compatibility.

A replacement breaker has to fit the existing panel, and a relay has to fit the cut out and the scheme. A firmware or communication mismatch can leave a correct device unusable on the day.

What every protection request needs

1. Device type and the system voltage it serves
2. Rated current and the short circuit breaking or withstand values required
3. The protection scheme and functions needed, and the scheme it must integrate with
4. Auxiliary supply voltage and communication protocol
5. Whether this replaces an existing device, with its nameplate or model if known
6. Quantity, destination, required delivery date and acceptable condition